This investigation is interested in exploring how a single essential amino acid, specifically L-tryptophan, affects protein metabolism in the liver. In earlier reports from our laboratory we have described that L-tryptophan rapidly stimulates hepatic polyribosomal aggregation and protein synthesis. This effect appears to be related to alterations in both transcriptional and posttranscriptional controls. Our present proposal plans to explore at the cellular and subcellular levels how L-tryptophan may act, possibly directly on the nucleus (nuclear membrane), to stimulate enhanced nucleocytoplasmic translocation of mRNA. Such information may offer basic insight as to how an important dietary component, as exemplified by L-tryptophan, may play a regulatory role in mammalian liver protein metabolism.